FIGS. 1a, 1b and FIGS. 2a, 2b show a conventional longitudinal type thermal treatment apparatus and a conventional load locking thermal treatment apparatus respectively.
A heater (2) is located around a reaction chamber (1) made of a high-purity material such as quartz and the like, and an opened end of the reaction chamber (1) is sealed by a seal flange moved by a transfer system (not shown). A mobile section and the seal flange moved by the transfer system are connected by a spring member, so that it makes the sealing condition between the seal flange and the reaction chamber better. Because a pressure inside the reaction chamber during a process is slightly the same as an outer pressure, the spring member is required at least such resiliency that the spring member slightly pressurizes the seal flange onto the reaction chamber through a sealant. The seal flange is composed of a quartz flange (9) and a metal flange (10), and the quartz flange is only emerged inside the reaction chamber while the reaction chamber has been sealed. A gas introducing inlet (6) is provided in the reaction chamber (1), and communicating this with another closed end of the reaction chamber along a side wall outside the chamber, then a gas is introduced into the chamber through there. A gas vent (7) is provided about the opened end of the reaction chamber, and the gas is vented through there. A boat table (5) and a boat (3) supporting, like a multi layer, a plurality of thermal treatment sections (4) are provided on the seal flange, and they are moved into and out from the reaction chamber by the transfer system.
When the boat has been moved out from the reaction chamber (1) (FIG. 1b) by the transfer system, workpieces are set on the boat. The boat is moved into the reaction chamber by the transfer system, the flange is sealed and the reaction chamber is also sealed. An inactive gas, such as nitrogen gas, is introduced from the gas introducing inlet, and an atmospheric compound mixed into the chamber during moving the boat is purged. Achieving the workpiece to the predetermined temperature by the heater, then a gas for the predetermined process is introduced. Oxigen and the like is introduced for the dry oxidation process. Vapour and the like, which is produced by burning oxygen and hydrogen at an outer combustion device (not shown) provided before the introducing inlet (6), is introduced for the wet oxidation process, or oxyphosphorus chloride (POCl.sub.3) and the like is introduced for the phosphorus dispersion process. The internal diameter of the introducing inlet is typically from about 10 mm to about 20 mm. The vent (7) is opened to the atmospheric environment and after an introduced gas contributes to the predetermined reaction, it is vented from the vent such that it is pressurized. The internal diameter of the vent is typically from about 10 mm to about 20 mm, and it is usually larger than the internal diameter of the introducing inlet. After completing the process, the introduction of a process gas is stopped, and after purging nitrogen gas and the like again, the boat is moved out from the reaction chamber by the transfer system.
Recently, according to the higher integration of a semiconductor device, in order to prevent an unpredictable oxidation caused by atmospheric compounds (oxygen, aqueous vapour and the like) and a residual process gas inside the reaction chamber after a process, the load locking thermal treatment apparatus has been developed. The examples are shown in FIG. 2a and FIG. 2b. A transfer system comprising a ball screw (13), a mobile section (12) and the like is set in a transfer system containing chamber (11) to seal to the atmosphere. The transfer system containing chamber (11) has a vent (15) to evacuate inside the chamber (11). Carring out a process at the atmospheric pressure, then a force is produced to open and to push the sealed flange by the pressure difference between the pressure inside the reaction chamber and the pressure inside the transfer system containing chamber. Thus, the sealed flange and the mobile section (12) are connected by a rigid member without the spring member and the pressure inside the transfer system containing chamber (11) is maintained about the atmospheric pressure by introducing the high purity nitrogen gas after evacuating, only during the process or all the time. The open section (14) is provided for moving a workpiece into or out from the transfer system containing chamber (11) and is connected with a front room (17) through a gate valve (16). A carrier system is contained to move the workpiece into or out from the boat from the open section in the front room. A metal manifold (23) having a vent (7b) is provided by connecting with the reaction chamber to evacuate the inner section of the reaction chamber comprising a high purity material such as quartz, and this manifold has a cooling section (3b). After completing the process, evacuating the inner section to about 10.sup.-6 torr by the evacuating system connecting to the vent (7b), unloading the boat, then the workpiece is taken out.
The metal manifold has been provided to evacuate the inner section of the reaction chamber for the load locking thermal treatment apparatus which has been developed to embody the treatment of a higher integrated device, however, a heavy metal contamination is caused to the workpiece thereby and this causes to retrograde the performance of the apparatus. Because the oxidation process is carried out by a high temperature such as typically about 1000.degree. C., its thermal radiation greatly affects. It may not be escaped that a metal contamination becomes to be larger than a metal contamination caused by an apparatus whose entire surface inside the reaction chamber is quartz such as a conventional oxidation diffusion apparatus, even if a cooling section is provided. Additionally, if over cooling is done, then vapour and the like will be condensated with dews on the surface inside the manifold at the wet oxidation, and it will exert further serious bad influences such as the metal corrosion and the like. Also, the thermal diffusion from the lower section of the heater becomes larger by the cooling, and it then causes the average thermal characteristic of the heater to be worse.
If the transfer system containing chamber is filled by high purity nitrogen gas after evacuating, the degree of cleanliness of the environment in the apparatus has a limit depended on the degrees of cleanliness of a supplied nitrogen gas and a gas supplying system. In order to respond to the request to a device of the further degree of integration, the pressure in the transfer system containing chamber is required to maintain in the high vacuum environment below 10.sup.-7 tort for further reducing the densities of residual oxygen, vapour and the like. If the environment of the transfer system containing chamber becomes the state of the atmospheric pressure by nitrogen gas during the process below the atmospheric pressure and the evacuation is done after completing the process, the throughput by the apparatus decreases and the cost of the supplied high purity nitrogen gas increases. If the mobile section and the seal flange are connected by a rigid member each other, the accuracy of the stop position of the mobile section and the degree of the parallelization between the seal flange and the interfacing surface should be strictly monitered, and thus the manufacturing cost can increase and the great skill is also required to incorporate again after the reaction chamber maintenance.